Abstract
The potential for contaminants to enter the lake shore environments of Lake Wanaka and Lake Wakatipu is an emerging problem for environmental managers within the Queenstown Lakes District of New Zealand. As population in the Queenstown Lakes District increases so too does the demand for more urbanised areas for housing, transport, commercial activities and industrialisation. This increase of urban area increases the proportion of land covered in impervious surfaces facilitating the transport of contaminants such as organic nutrients, heavy metals and pathogens to the aquatic environment. To assess the impacts of urbanisation on the lakeshore environment and the potential for using invertebrate community composition as a biomonitoring tool, a small scale community analysis of littoral-benthic invertebrates was conducted in Lake Wanaka between impacted and non-impacted sites. Secondly, a larger scale community analysis was conducted in both Lake Wanaka & Lake Wakatipu at varying distances to stormwater outlets entering the lake. A higher taxonomic resolution investigation of the family Chironomidae was also undertaken for the initial sampling effort in Lake Wanaka to assess changes in Chironomidae assemblages in relation to urban impact.
Littoral-benthic invertebrate communities of both lakes at sites considered higher levels of impact showed an overall decline in relative abundance of taxa belonging to the orders Ephemeroptera, Plecoptera & Trichoptera (EPT) and the Dipteran family Chironomidae, than sites considered less impacted. These communities also displayed a shift towards a more homogenous community composition, dominated largely by Oligochaeta worms and the freshwater snail Potamopyrgus antipodarum. The higher resolution identification of Chironomidae assemblages within Lake Wanaka showed that the subfamily Orthocladiinae were negatively responding to urban impact, with lower abundances observed at sites considered impacted than at those which were considered non-impacted.
The results of this study suggest that littoral-benthic invertebrate communities do indeed show clear responses in their composition in regards to increasing levels of urban impact. These responses suggest that the decline of EPT taxa & Orthocladiinae, and homogenization of the community towards P. antipodarum and Oligochaeta dominance may provide useful biomonitoring tools to environmental managers of lakes in the Queenstown Lakes District.